1. Field of the Invention
The present invention generally relates to imaging and, more particularly, to an operation device including a touch switch and an image processing apparatus including the operation device.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2009-88759 discusses a multifunction peripheral (MFP) which includes an image reading unit. The device includes a reading unit, which is configured to read an image of a document set on a reading surface, and a pressing plate, which can open on the reading surface. On an upper surface of the pressing plate, an operation unit, which includes a plurality of input keys, and a display device, such as a liquid crystal display (LCD) panel, are provided.
U.S. Patent Application Publication No. 2009/0033636 Al discusses a capacitive touch panel input device. The capacitive touch panel input device includes a substrate and a spacer. A plurality of sensor electrodes is implemented on the capacitive touch panel input device. The spacer is set on each sensor electrode.
Japanese Patent Application Laid-Open No. 11-283425 discusses an illumination device (a backlight), which illuminates an LCD display device that displays a character and a graphic with light from the back thereof. Another conventional method discussed in the Japanese Patent Application Laid-Open No. 2009-88759 includes an operation unit that has a structure of a mechanical-contact key, such as a tactile switch. However, in terms of lower costs and appropriate component arrangement and design, the operation unit can be replaced with the capacitance touch switch, such as the one discussed in the U.S. Patent Application Publication No. 2009/0033636 A1.
In this case, the visibility of the switch can be increased by using a backlight (an illumination device) provided behind the switch. In addition, in this case, the operability of the capacitive touch panel input device also can be increased by turning off the backlight if it is not necessary to use the backlight.
The above-described structure of the conventional operation unit may not be implemented if uneven luminosity occurs and if a large number of light sources are required. In other words, in order to implement the above-described structure of the conventional operation unit, if the area of a region of the touch switch to be illuminated with light is large, it is required to illuminate the touch switch from behind with light intense enough to increase the visibility of the touch switch to a highly visible level and to reduce uneven luminosity with the smallest possible number of light sources.
The illumination device discussed in the Japanese Patent Application Laid-Open No. 11-283425 forms a reflection surface in a region of a light guide plate (8) having a limited area to illuminate the touch switch with highly intense light. In addition, an exit window (11), which has a white cover frame, is provided limitedly for the display range to prevent leaking light. However, in order to illuminate the necessary range of a large area with light by using the smallest possible number of light sources, the structure of the operation unit discussed in the Japanese Patent Application Laid-Open No. 11-283425 may not be useful enough.
In other words, a part of the light guided to a side of the light guide plate (8) may exit from another side thereof. Accordingly, the light utilization efficiency may become low. In addition, in this case, the brightness may become uneven.
The conventional method discussed in the Japanese Patent Application Laid-Open No. 11-283425 implements illumination of the touch switch with sufficiently intense light by using two light sources provided at both ends of the switch illumination range. However, using two light sources is less useful than the single light source configuration in terms of lower costs and the resulting highly free arrangement of components.
Furthermore, it may be difficult to apply the illumination device discussed in the Japanese Patent Application Laid-Open No. 11-283425 as a backlight for illuminating the capacitance touch switch discussed in the U.S. Patent Application Publication No. 2009/0033636 A1 with light because of the following reason.
More specifically, if the structure discussed in the U.S. Patent Application Publication No. 2009/0033636 A1 is employed, an air gap may arise in or around the exit window 11. If an air gap exists between the surface of a touch panel, which is touched by an operator with his finger, and an electrode, it may become difficult to detect the capacitance.
Accordingly, if an electrode is provided in the structure discussed in the U.S. Patent Application Publication No. 2009/0033636 A1, it is required to provide the electrode outside the exit window (11) (i.e., on the back side of an LCD display device (12). Therefore, the electrode may interfere with the light emitted from the backlight. Accordingly, in this case, the display may not be appropriately executed.